1. Technical Field
The present invention relates to an electrode for polymer electrolyte fuel cells, and in particular, relates to a technique in which a catalyst functions efficiently.
2. Background Art
A polymer electrolyte fuel cell is formed by laminating separators at both sides of a tabular membrane electrode assembly (MEA). The membrane electrode assembly is generally a laminated body having a polymer electrolyte membrane placed between a cathode side catalytic layer and an anode side catalytic layer, and having a gas-diffusion layer laminated at the outside of each catalytic layer. In such a fuel cell, hydrogen gas supplied through a separator plate arranged at the cathode side and an oxidizing gas supplied through a separator plate arranged at the anode side electrochemically react and thereby generate electricity.
During operation of the fuel cell, electrons generated in an electrochemical reaction are conducted between an electrode catalytic layer and a separator, and at the same time, fuel gas and oxidizing gas are diffused through a gas-diffusion layer. In an electrode catalytic layer of the anode, fuel gas reacts and generates protons and electrons, and in an electrode catalytic layer of the cathode, oxygen, protons, and electrons react and generate water. An electrolyte membrane conducts protons and thereby generate electricity through the electrode catalytic layer of the anode and the cathode.
In the anode side, protons and electrons are generated under coexistent conditions of a catalyst, electron conducting particles, and an electrolyte. That is to say, hydrogen gas is reduced under conditions in which an electrolyte which conducts protons, electron conducting particles which conducts electrons, and a catalyst coexist.
An electrode catalytic layer is generally formed by a method in which electron conducting particles carrying catalyst particles on their surfaces such as Pt, and an electrolyte comprising an ion conducting polymer, are mixed together in a solvent to form a catalyst paste, and this catalyst paste is coated on a membrane, a carbon paste, or a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) sheet, and is dried. Therefore, generation efficiency tends to be increased as the amount of a catalyst carried by the electron conducting particles is increased. Both the cathode and the anode show the same tendency as described above.
However, in a conventional electrode for fuel cells as described above, utilization ratio of catalyst metal on electron conducting particles carrying catalyst is low, and an excessive amount of carried catalyst must be used. Furthermore, because this catalyst is composed of a rare metal such as Pt, the manufacturing cost of the fuel cell is increased as the amount of the catalyst carried by electron conducting particles is increased.
Therefore, an object of the present invention is to provide an electrode for polymer electrolyte fuel cells in which generation efficiency can be improved without increasing the amount of catalyst carried by electron conducting particles. Furthermore, an object of the present invention is to provide a method of producing electrodes for polymer electrolyte fuel cells efficiently.